JPH087830A - Atmospheric pressure ionization mass spectrometry device - Google Patents

Abstract

PURPOSE:To prevent the ruduction of ion passing amount by preventing and removing the attachment and the accumulation of neutral molecules to an orifice. CONSTITUTION:In a buffer chamber 29 or in a high vacuum chamber 30, a filament 24 to discharge thermoelectrons, and accelerating electrodes 25 to accelerate the thermoelectrons discharged from the filament 24 to an orifice, are provided. Consequently, the accelerated thermoelectrons, and the secondary electrons produced by striking the thermoelectrons to the inner wall, strike to a skimmer, and the neutral molecules attached and accumulated to the orifice are removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency inductively coupled plasma mass spectrometer (ICP-MS), an electrospray mass spectrometer (ESP-MS), an atmospheric pressure chemical ionization mass spectrometer (APCI-MS) and the like. The present invention relates to a pressure ionization mass spectrometer.

[0002]

2. Description of the Related Art In these mass spectrometers, ionization of a sample is performed under atmospheric pressure, while mass spectrometry of ions is 1
It must be performed by a mass spectrometer arranged in a high vacuum of about 0 ⁻⁴ to 10 ⁻⁶ torr. Since holes for passing ions must be provided between the two spaces having such a large pressure difference, in these mass spectrometers, the space between the outside and the high vacuum chamber in which the mass spectrometer is arranged is large. To 1
One or two buffer chambers are provided so that two or three stages of differential exhaust can be performed. Sampling cones and skimmers having orifices (ion passage holes) are provided on the partition walls between the outside and the buffer chambers and between the buffer chambers, and these orifices maintain the vacuum difference between the chambers as much as possible. It should be as small as possible.

[0003]

The ions of the sample generated at atmospheric pressure are accelerated by the electric field applied to the sampling cone, skimmer, etc., and are introduced toward the mass analyzer. Due to the difference, neutral molecules are also attracted in the same direction. These neutral molecules interfere with the passage of ions by adhering and accumulating around the orifices of sampling cones, skimmers, etc., narrowing the orifices, and charging up (charging) due to the accumulation of ions in the insulating part of the skimmer. .

The present invention has been made to solve such a problem, and an object of the present invention is to prevent and remove the adhesion and deposition of such neutral molecules to achieve a highly sensitive measurement. An object of the present invention is to provide an atmospheric pressure ionization mass spectrometer capable of performing.

[0005]

SUMMARY OF THE INVENTION An atmospheric pressure ionization mass spectrometer according to the present invention made to solve the above problems applies a positive DC voltage to a sample ionized in the atmosphere or in a low vacuum chamber. In an atmospheric pressure ionization mass spectrometer for mass spectrometry, which is introduced into a high vacuum chamber through one or more buffer chambers that are separated by a partition having an orifice and in which differential evacuation is performed, a) buffer chamber or high vacuum chamber A filament for emitting thermoelectrons, and b) an electron optical system for accelerating thermoelectrons emitted from the filament toward the orifice.

[0006]

In order to reduce a large difference in vacuum degree between the outside (in the atmosphere) and the high vacuum chamber or between the low vacuum chamber and the high vacuum chamber, one or a plurality of buffer chambers are provided between them. , Differential evacuation is performed. Partition walls are provided between the atmosphere or the low vacuum chamber and the buffer chamber, and between the buffer chamber and the high vacuum chamber (and between the buffer chambers when there are a plurality of buffer chambers). Is provided with an orifice (ion passage hole) for passing ions. A positive DC voltage is applied to these partition walls.

The sample is ionized in the atmosphere or in a low vacuum chamber, passes through the orifice, and enters the buffer chamber. When a plurality of buffer chambers are provided, they further pass through the same orifice and sequentially pass through the buffer chambers. Then, the ions are finally introduced into the high vacuum chamber, where mass spectrometry is performed.

Here, due to the pressure difference between the atmosphere or the low vacuum chamber and the buffer chamber, and between the buffer chamber and the high vacuum chamber (or between the buffer chambers when there are a plurality of buffer chambers), Neutral molecules that have not been ionized are introduced toward the high vacuum chamber as well as the ions. However, since the neutral molecules are not repelled by the DC voltage applied to each partition, they are attached and deposited around the orifice.
On the other hand, the thermoelectrons generated by the filament are
The neutral molecules accelerated by the electron optical system and colliding with the orifice and thus attached and deposited are removed by sputtering. Further, thermions accelerated by the electron optical system collide with the wall of the buffer chamber or the space connected to the buffer chamber to generate secondary electrons, and the secondary electrons are positive DC applied to the partition walls of each room. There is also the effect of being accelerated by the voltage and colliding with the orifice for sputtering.

The "buffer chamber or high vacuum chamber" described above as a place for arranging the filament includes not only the interior of the buffer chamber or the high vacuum chamber itself, but also a space connected to these chambers. For example, a passage between a buffer chamber or a high vacuum chamber and a pump for performing the vacuum drawing is also included.

[0010]

EXAMPLE As an example of the present invention, an electrospray mass spectrometer (ESP-M) using a magnetic field type mass spectrometer is used.
S) will be described with reference to FIG. In the present mass spectrometer, a sample is jetted from the needle 11 to which a high voltage is applied at atmospheric pressure toward the counter electrode 14, and at the same time, nitrogen gas or the like is jetted from around the needle 11 to atomize and ionize the sample 12. (In FIG. 1, a symbol with + inside the circle represents an ion). The ionized sample 12 enters the mass spectrometer main body 13 from a sampling orifice 14 a provided in the counter electrode 14.

Inside the body 13, two partition walls 15 and 16 are provided.
Skimmers 15a and 16 having ion passage holes (orifices) at the tips of both partition walls 15 and 16, respectively.
a is provided. The first buffer chamber 28 between the counter electrode 14 and the first partition 15 is exhausted by a rotary pump (RP), and the second buffer chamber 29 between the first partition 15 and the second partition 16 and 2 The high vacuum chamber 30 after the th partition is provided with a diffusion pump (DP) or a turbo molecular pump (TMP) provided in each.
Exhausted by. Exhaust pipes 21, 22 and 23 connect the buffer chambers 28 and 29 and the high vacuum chamber 30 to the pumps RP, DP and DP.

The ions that have entered the body 13 are both skimmers 1.
Ion optical system 17 in high vacuum chamber passing through 5a and 16a
After being focused by and passing through the passage hole 18, mass analysis is performed by the magnetic field type mass analyzer 19.

However, some of the samples ejected from the nozzle 11 are not ionized and enter the main body 13 in the state of neutral molecules (represented by the symbol N in the circle in FIG. 1). To do. Some of such neutral molecules are skimmer 15
a and 16a, and is deposited. In particular, if such adhesion / deposition occurs near the orifice, it narrows the orifice, making it physically difficult for ions to pass through, and it also charges up due to the accumulation of neutral molecules and ions in the insulating part, disturbing the electric field. This also hinders the correct passage of ions.

Therefore, in the mass spectrometer of this embodiment, the second
A filament 24 and an accelerating electrode 25 are provided in the exhaust pipe 22 for the buffer chamber 29. At the time of mass spectrometry, a thermal current is supplied from the control unit 27 to the filament 24, and a positive DC voltage is applied to the accelerating electrode 25. As a result, thermoelectrons are emitted from the filament 24, and the thermoelectrons are accelerated by the acceleration electrode 25 and collide with the skimmers 15a and 16a. Further, the accelerated thermoelectrons collide with the tube wall of the exhaust pipe 22 and the inner wall of the main body 13 to generate secondary electrons,
These secondary electrons are also accelerated by the positive DC voltage applied to the skimmers 15a and 16a,
It collides with 16a. The collision of these electrons removes (sputters) the neutral molecules adhering to and depositing on the skimmers 15a and 16a, thereby eliminating the clogging of the orifice and the charge-up. The filament 2 used here
4 may be shared with the filament of the ion gauge.

In FIG. 1, the filament 24 is provided only in the second buffer chamber 29, but as shown in FIG.
The same filament 34 and accelerating electrode 35 may also be provided on 0. In this case, not only the skimmers 15a and 16a but also the ion optical system 17 has an effect of preventing the attachment of neutral molecules.

When the positive voltage applied to the skimmers 15a and 16a is sufficiently high, as shown in FIG. 3, the filaments 44 and 4 are provided without providing an accelerating electrode.
Only 5 may be placed in the buffer chamber 29 and / or the high vacuum chamber 30. However, as shown in FIG. 4, when the quadrupole mass spectrometer 59 is used, the skimmer voltage is low, so that the acceleration electrode 65 is necessary.

[0017]

In the atmospheric pressure ionization mass spectrometer according to the present invention, the thermoelectrons generated by the filament and accelerated by the electron optical system, and the thermoelectrons generated by colliding with the exhaust passage, the wall of the buffer chamber and the like. The generated secondary electrons collide with the orifice to remove neutral molecules adhering and accumulated in the vicinity of the orifice and clean the same. As a result, the number of ions blocked on the way is reduced and more ions are guided to the mass spectrometer, so that highly sensitive mass analysis can be performed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an electrospray mass spectrometer using a magnetic field type mass spectrometer that is a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing another configuration of the first embodiment.

FIG. 3 is a schematic configuration diagram showing still another configuration of the first embodiment.

FIG. 4 is a schematic configuration diagram of an atmospheric pressure ionization mass spectrometer using a quadrupole mass spectrometer that is a second embodiment of the present invention.

[Explanation of symbols]

11 ... Sample / gas injection nozzle 13 ... Mass spectrometer main body 14 ... Counter electrode 14a ... Sampling orifice 15, 16 ... Partition walls 15a, 16a ... Skimmer 17, 57 ... Ion optical system 18 ... Ion passage hole 19 ... Magnetic field type mass analyzer 21, 22, 23, 61, 62, 63 ... Exhaust pipe 24, 34, 64 ... Filament 25, 35, 65 ... Accelerating electrode 28, 29, 68 ... Buffer chamber 30, 70 ... High vacuum chamber 59 ... Quadrupole type Mass spectrometer RP ... Rotary pump DP ... Diffusion pump

Claims (1)

[Claims] 1. A high-vacuum chamber through one or more buffer chambers in which a sample ionized in the atmosphere or in a low-vacuum chamber is separated by a partition having an orifice to which a positive DC voltage is applied and differential pumping is performed. In an atmospheric pressure ionization mass spectrometer that performs mass spectrometry by introducing into a chamber, a) a filament that emits thermoelectrons in a buffer chamber or a high vacuum chamber, and b) directs thermoelectrons emitted from the filament toward an orifice. An atmospheric pressure ionization mass spectrometer, comprising: